1. Field of the Invention
The present invention relates to a magnetoresistive element such as a tunnel magnetoresistive element or a giant magnetoresistive element, a method of manufacturing the same, and a magnetic multilayered film manufacturing apparatus and, more particularly, to a magnetoresistive element such as a tunnel magnetoresistive element or a giant magnetoresistive element usable for the magnetic head of a magnetic disk drive or a magnetic random access memory, a method of manufacturing the same, and a magnetic multilayered film manufacturing apparatus.
2. Description of the Related Art
A conventional magnetic disk drive uses a giant magnetoresistive element or a tunnel magnetoresistive element for its magnetic head.
A giant magnetoresistive element has an antiferromagnetic layer, ferromagnetic fixed layer, nonmagnetic conductive layer, and ferromagnetic free layer. A tunnel magnetoresistive element has an antiferromagnetic layer, ferromagnetic fixed layer, tunnel barrier layer, and ferromagnetic free layer.
The ferromagnetic fixed layer of the giant magnetoresistive element or tunnel magnetoresistive element can use at least one of Fe, Co, and Ni as the ferromagnetic material. The antiferromagnetic layer can use an antiferromagnetic material such as PtMn or IrMn which is obtained by adding a precious metal element to Mn.
However, the conventional magnetoresistive element has poor stability against heat. When the magnetoresistive element is heated to, for example, 300° C. or more, the MR ratio degrades considerably.
Magnetoresistive elements described in Japanese Patent Laid-Open Nos. 2000-67418 (U.S. Pat. No. 6,052,263), 2003-258335, 2003-304012, and 2005-203790 have improved the thermal stability to some extent but have not achieved a sufficient MR ratio for practical use.
The present inventors found, by studies and analyses, the following causes of poor thermal stability of the magnetoresistive element.
For example, in a magnetic head manufacturing process, a tunnel magnetoresistive element undergoes annealing at 250° C. to 300° C. in a high magnetic field of several T (tesla) for several hrs after film formation to magnetize a PtMn layer serving as an antiferromagnetic layer. For a magnetic random access memory, annealing is performed in a post-process at a temperature higher than 300° C., in addition to the annealing in a high magnetic field after film formation. In the annealing process, manganese (Mn) in the above-described antiferromagnetic layer diffuses to other layers such as a ferromagnetic fixed layer and a tunnel barrier layer due to the heat. This degrades the magnetic characteristic of the ferromagnetic fixed layer or the tunnel barrier effect of the tunnel barrier layer. As a result, the MR ratio of the magnetoresistive element degrades.
The ferromagnetic fixed layer or tunnel barrier layer preferably has a crystal structure such as a microcrystalline, polycrystalline, or single-crystal structure. The diffused manganese (Mn) is supposed to adversely affect the crystalline ferromagnetic fixed layer or crystalline tunnel barrier layer and consequently degrade the MR ratio.
Particularly when the ferromagnetic fixed layer has an SAF (Synthetic Anti-Ferromagnet: antiparallel coupling element) structure including three layers: a crystalline first ferromagnetic fixed layer containing cobalt-iron (CoFe) and located on the substrate side, a first nonmagnetic intermediate layer 14 made of, for example, ruthenium (Ru) and located on the ferromagnetic fixed layer, and a crystalline second ferromagnetic fixed layer containing crystalline cobalt-iron-boron (CoFeB), the thermal diffusion of manganese (Mn) in the antiferromagnetic layer adversely affects the ferromagnetic fixed layer, and as a result, the MR ratio of the magnetoresistive element degrades.
The above-described thermal diffusion also occurs in a giant magnetoresistive element.
It is an object of the present invention to provide a magnetoresistive element such as a tunnel magnetoresistive element or a giant magnetoresistive element having a high thermal stability and a high MR ratio, and a method of manufacturing the same.